Single reel data tape cartridges, known as 3480 type cartridges, include a reel containing a plurality of layers of magnetic tape with a leader block attached to the free end of the tape as it extends from the reel. The cartridge is generally rectangular except for one corner which is angled and includes a leader block window. The leader block window holds the leader block and permits the tape to exit from the cartridge for threading through a tape drive when the leader block is removed. When the leader block is snapped into the window, the window is covered.
The leader block is generally rectangular and has a cutout which combines with a pin to hold the tape. The front surface of the leader block includes a slot for engaging an automatic threading apparatus in a reel-to-reel magnetic tape drive apparatus. The front surface of the leader block is generally cylindrical and has a rounded boss which engages with an inclined surface of the corner of the cartridge. The rear surface is rounded to form a portion of an arc of a radius to match the periphery of the takeup reel hub in the tape drive apparatus as the leader block fits into the slot in the hub. A compliant section may be formed on the leader block to permit the leader block to compress at its rear surface to accommodate especially the first layer of tape when the tape is wound onto the take-up reel.
The tape drive apparatus includes a threading apparatus for connection to a single reel tape cartridge. The drive apparatus includes a drive motor for the supply reel mounted beneath a base plate so that its shaft extends normal to and slightly above a surface of the base plate. A take-up reel is mounted on the base plate and is attached to the motor. The cartridge reel, when coupled to the motor, lies in substantially the same plane as a hub of the take-up reel so that the tape moves in a plane normal to both motor shafts when being transported. After the threading of the tape, transfer of the tape between the supply reel and the take-up reel is achieved by controlling the driving motors for the reels. The tape passes a roller guide, an air bearing guide, a magnetic transducer head, a second air bearing guide, and a roller of a tension transducer.
The cartridge is formed of a base and a cover. The base includes a rear wall, two opposing side walls, a front wall, and a major, lower wall connecting the rear, front, and side walls. The cover includes a rear wall, two opposing side walls, a front wall, and a major, upper wall connecting the rear, front, and side walls. The upper wall has an upper surface and a lower surface. The upper surface has a substantially rectangular recessed portion which is adapted to receive an identifying label and to receive ribs external to the base of an adjacent cartridge when a plurality of cartridges are stacked one on top of the other. The thickness of the upper wall is substantially constant, generally being 0.20 cm (0.08 in) thick except for the area of the 0.05 cm (0.02 in) deep recess.
Strengthening ribs are formed on the inner surfaces of the cover and the base. However, during the molding of the base, sink occurs in the base on its outer surface. This yields an undesirable unsightly visible mark on the outside of the base corresponding to the shape of the strengthening ribs. This mark is more visible in opaque bases than in translucent bases. The existence of sink impairs the salability of the finished product. The sink is caused by excess shrinkage at the thicker interface between the strengthening ribs and the surface of the cover and base.
There is a need to provide cartridge housing components that do not have aesthetically undesirable sink marks. No known cartridges formed by molding are free from sink problems.